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Astron. Astrophys. 347, 617-629 (1999) AcknowledgementsThe topic of this paper has been seeded by fruitful discussions with Prof. Dr. L. A. Willson. We would like to thank Christiane Helling, Dr. Andrej Fokin and Prof. Dr. P. Cottrell for their valuable comments on the manuscript and the hospitality of the Department of Physics and Astronomy at the University of Canterbury, New Zealand, where this paper was completed. This work was supported by the German Deutsche Forschungsgemeinschaft, DFG project number Se 420/15-1. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1999 Online publication: June 30, 1999 ![]() |